Understanding the AIRS, ARM, and MODIS cloud products by cross-comparison
| Kahn, Brian | Jet Propulsion Laboratory |
| Eldering, Annmarie | Jet Propulsion Laboratory |
Category: Cloud Properties
We present comparisons of the Atmospheric Infrared Sounder (AIRS) operational cloud top height (CTH) to the active surface-based measurements of the Atmospheric Radiation Measurement (ARM) program sites in the tropical Western Pacific. The agreement is found to be consistent to other comparisons of passive IR-derived CTH from other measurement platforms despite the nominal footprint size of 45 km at nadir view. Independent comparisons of CTH to the millimeter-wave cloud radar at Manus Island and the micropulse lidar at Nauru Island indicate that the CTH retrieved by AIRS is statistically significant at the 5% level or less for cirrus cases with an effective cloud fraction (ECF) of 0.05–1.0. This shows the utility of AIRS CTH for use in quantitative analyses. A radiative approach is used to compare the CTH and the ECF of AIRS to those retrieved by the Moderate Resolution Imaging Spectroradiometer (MODIS) through the “reconstruction” of a brightness temperature (BT) using CTH, ECF, and surface temperature. Since AIRS reports up to two cloud layers and MODIS only one, and MODIS observes at much smaller pixel sizes than AIRS, this leads to difficulties in comparing individual products such as CTH and ECF individually. We show through the reconstructed BT that AIRS and MODIS are generally consistent with each other in most cloudy scenes around the globe, with broken water clouds in the tropical and subtropical regions showing a consistent and peculiar discrepancy. This discrepancy is traced to an 11–micron window channel technique to retrieve MODIS CTH, indicating that caution must be used when using passive IR-derived cloud products for cloud scenes that are difficult to make with such measurements.
This poster will be displayed at the ARM Science Team Meeting.
